During casting in a continuous casting installation, liquid steel is cast from a distributor into a water-cooled, usually copper mould. During the continuous withdrawal of the strand from the mould, the mould is moved at a frequency of approximately 1 to 3 Hz in the strand withdrawal direction. As a rule a lubricating film is maintained between the steel and the inside of the mould wall. The cooling of the steel by the mould walls leads to the formation of a steel strand having solidified steel shells and a steel liquid core. The thus partially solidified steel strand is drawn by means of suitable withdrawal means from the mould, being at the same time supported and guided by rollers disposed below the mould.
In the practical operation of such a continuous casting installation from time to time unforeseeable malfunctions occur which sometimes result in liquid steel breaking through the solidified strand shell. Such breaches are attributed to cobbles (adhesion) between the steel and the cooled mould wall. Due to the withdrawal forces acting on the partially solidified strand, the strand shell is torn open in the zone of the cobbles. If then that place is not made strong enough again by cooling before leaving the mould, the liquid steel breaks through and flows into the installation. As a result, parts of the installation disposed below the mould, such as supporting and guide rollers and supporting constructions are often damaged to such an extent as to be no further use, and have to be replaced by new parts. This means that the installation has to be stopped, sometimes for days, with consequent loss of production. Continuous casting installation operators are therefore anxious to avoid such break-outs to the greatest possible extent.
For example, to prevent break-outs it has already been proposed to measure the changes in the withdrawal forces at the first segments of a strand guide adjoining the mould and to use the measured values to control the casting process. If given limit values are not reached, the casting process is slowed down or even interrupted (DE PS 29 23 900).
It is also known (DE PS 25 01 868) to monitor the distribution of the heat flux density on the mould wall during the casting process. The heat flux density is determined indirectly by measuring the expansion of the shaping mould wall at a number of portions thereof. The signals obtained are linked to one another in order to control in dependence thereon the strand withdrawal speed and the steel supply to the mould. That process does not relate, therefore, to the detection of cobbles preceding break-outs, but to the detection of the distribution of the heat flux density over the mould height, to enable the casting process to be controlled in dependence thereon.
In another prior art process (EP A3 0 389 139) the heat flux is determined at different heights of the mould, and the distance between the zone of maximum heat flux and the level of the bath of molten metal is used as a criterion to determine whether a break-out is starting.
The invention starts from a process for the casting of metals in a continuous casting installation, wherein the strand is continuously withdrawn from the mould and the casting process is controlled in dependence on stresses occurring in the continuous casting installation during the withdrawal of the strand.
It is an object of the invention to provide in such a process steps which enable strand break-outs to be avoided in a simple manner.